Disordered superconductors: Third-harmonic response and charge fluctuations

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The scientific aim of the present project is related to an understanding of the influence of disorder in cuprate superconductors with regard to the following aspects:(a) Signatures of collective modes in the third-harmonic response of pump-probe experiments. Here we are planning the investigation of the corresponding spectra for d-wave superconductors under the influence of disorder. In particular, we are interested in the contribution of amplitude- , charge and phase modes on the low energy response where we also intend to analyze the influence of long-range Coulomb interactions. We aim to explain the experimentally observed polarization dependence as well as the phase of the third harmonic response in cuprate superconductors which is substantially different from that expected for s-wave systems.(b) Structure of charge-order and charge density wave fluctuations. Recent experiments have revealed the presence of short-range charge fluctuations in a large part of the phase diagram which may account for the unusual transport properties in the strange metal phase. Within the present project we intend to study the structure of such fluctuations in disordered strained films where transport and RIXS experiments have revealed a nematic ground state.On both topics we have a long-standing cooperation with the Solid State Theory group of the Department of Physics at the University of Rome ’La Sapienza’ which we aim to continue within the present proposal.